Effect of intermittent aeration regulation of a multi-soil-layering system on domestic wastewater treatment in Thailand

Abstract

This study investigated the effect of aeration of a multi-soil-layering (MSL) system on domestic wastewater treatment. The MSL system was constructed in a 100×200×150 cm concrete tank. Clayey soil was mixed with sawdust and iron scraps at a ratio of 75:10:15, respectively, based on dry weight. The soil mixture was filled into the tank as blocks, thus forming a brick-like layer pattern. The void spaces between the soil blocks were filled with zeolite. Combined toilet and cafeteria wastewater, which was pre-treated by using settlement tanks, was discharged periodically to the MSL system. The loading rate of wastewater varied from 100 to 600 l m −2 d −1. Aeration was applied to the MSL system at rates of 0, 4000 and 20,000 l m −3 d −1. The results revealed that the aeration assists the removal efficiency of biochemical oxygen demand (BOD 5), chemical oxygen demand (COD) and soluble reactive phosphorus (SRP). When the MSL system was aerated at a rate of 4000 l m −3 d −1 for 1 week, BOD 5, COD and SRP removal efficiencies reached 87.4, 53.2 and 80.3%, respectively. However, at this aeration rate, the efficiency of total nitrogen (TN) removal declined to −26.7%. Aeration at a rate of 20,000 l m −3 d −1 for 3 days was more effective for enhancing BOD 5, COD, TN and SRP removals than aeration at the rate of 4000 l m −3 d −1. The removal percentages of BOD 5, COD, TN and SRP at values of 92.2, 73.3, 15.0 and 74.7, respectively, were recorded. Two months of non-aeration decreased the COD removal efficiency to <27%, whereas the BOD 5, TN and SRP removals were at high levels of 82.1, 65.3 and 83.0%, respectively. This suggested that COD removal needed more intensive aeration than the other parameters. Aeration at a rate of 20,000 l m −3 d −1 alternated with 2 months of non-aeration is appropriate for operating the tested MSL system in Thailand.